Mike Flynn, President Trump's former national security adviser, refused an additional request to appear before the Senate Intelligence Committee as a witness, according to a report Tuesday.

Flynn previously refused to adhere to a subpoena in May, using his Fifth Amendment rights, from the Senate intelligence panel which is investigating if any collusion occurred between the Trump campaign and Russia during the 2016 election.

The committee has since requested again that Flynn appear as a witness and he has declined again, according to CNN.

After the committee issued these two subpoenas, Flynn did submit 600 pages of documents to the committee. Included were personal and business records.

Flynn stepped down as a national security advisor in February after it was revealed he lied about his communications with the Russian ambassador to the U.S.

Furthermore, the House Intelligence Committee, which is also investigating collusion between Russia and the Trump campaign, subpoenaed Flynn. Although Flynn has offered to testify for the House and Senate committees for immunity, the committees have refused.